Pressure sensors that use the piezo resistance effect of semiconductors are small, light, and have high sensitivity, and thus are used widely in fields such as industrial instruments, medicine, and the like. In this type of pressure sensor, a strain gauge is formed on a semiconductor diaphragm. The strain gauge deforms depending on the pressure that is applied to the diaphragm. The change in resistance of the strain gauge due to the piezo resistance effect is detected to measure the pressure. In order to mitigate the stress from the package, the sensor chip wherein the diaphragm is formed is bonded to a base made out of, for example, glass. (Japanese Unexamined Patent Application Publication 2002-277337)
Here the structure of the pressure sensor will be explained using FIG. 5. FIG. 5 is a cross-sectional diagram illustrating the structure of a conventional pressure sensor. The sensor chip 10 is structured from a single crystal silicon substrate. Additionally, strain gauges 5 and 15, having the piezo resistance effect, are formed on the sensor chip 10. The center portion of the sensor chip 10 is etched to form a diaphragm 4. Here the center portion of the sensor chip 10 is etched to a tapered shape. Doing so increases the dimension of the opening of the diaphragm sensor to larger than the dimension of the diaphragm. A base 11 is bonded to the sensor chip 10. The base 11 is bonded to the sensor chip 10 at the peripheral portion of the diaphragm 4.
Japanese Unexamined Patent Application Publication 2002-208708 discloses a pressure sensor wherein, in order to mitigate the concentration of stresses, the edge portion of the sensor region side of the diaphragm is formed in an R shape.
It is necessary to increase the size of the diaphragm 4 in order to increase the pressure sensitivity of the pressure sensor. Additionally, it is necessary for the surface area of the bonding region (the bonded portion) to be large in order to ensure the bonding strength with the base 11. However, when the size of the sensor chip 10 is held constant, increasing the size of the diaphragm 4 in order to increase the sensitivity reduces the bonding region with the base, and increasing the size of the bonding region in order to increase the reliability of the bond reduces the size of the diaphragm 4. Consequently, there is a problem in that the size of the sensor chip 10 must be increased in order to both increase the pressure sensitivity and secure the bonding strength.
The present invention was created in order to solve this type of problem area, and the object thereof is to provide a small, high-performance pressure sensor, and provide a manufacturing method thereof.